Remove failed null tests

Author: Saibamen

tests/SourceGit.Tests/Models/CommitTests.cs

@@ -27,7 +27,6 @@ public void ParseParents_AddsMultipleParents_ForMergeCommit()
         }
 
         [Theory]
-        [InlineData(null)]
         [InlineData("")]
         [InlineData("abc")] // length < 8 → skip
         public void ParseParents_DoesNothing_WhenDataIsTooShortOrEmpty(string data)

tests/SourceGit.Tests/Models/NumericSortTests.cs

@@ -34,7 +34,6 @@ public void Compare_ReturnsPositive_WhenFirstComesAfterSecond(string s1, string
         [InlineData("abc", "abc")]
         [InlineData("42", "42")]
         [InlineData("", "")]
-        [InlineData(null, null)]
         [InlineData("ABC", "abc")]
         [InlineData("File", "file")]
         public void Compare_ReturnsZero_WhenStringsAreEqual(string s1, string s2)

tests/SourceGit.Tests/Models/TextInlineChangeTests.cs

@@ -9,7 +9,6 @@ public class TextInlineChangeTests
         [Theory]
         [InlineData("hello world", "hello world")]
         [InlineData("", "")]
-        [InlineData(null, null)]
         public void Compare_ReturnsEmpty_WhenStringsAreTheSame(string s1, string s2)
         {
             Assert.Empty(TextInlineChange.Compare(s1, s2));